This PR is a first step to addressing #68.
At the moment, these changes only check if the gracedb_client object on FinalSink is not None.
If it is None, we skip the upload, otherwise the code logic should execute as normal.
Additionally, we are able to specify a maximum of n attempts to upload triggers to GraceDb, with the default specified to n=3.
The benefit of this change is simply that we don't run n trials to try to upload each trigger when we know there is no available gracedb client (such as on OzStar), ultimately saving time and minimising the amount of unnecessary messages we add to our logs.